Resonant ion stimulated desorption of O+ from the TiO2(110) surface:: Effects of oxygenation and ion bombardment

The O+ desorption from reduced, oxygenated, and ion-bombarded TiO2(110) surfaces has been investigated during He+ irradiation. The O+ desorption is initiated by creation of an antibonding O 2s core hole state via quasi-resonant charge exchange with the He+ 1s state, followed by the intra-atomic Auger decay of the O 2s hole. Upon oxygenation of the reduced TiO2(110)surface, the O+ yield increases by one order of magnitude. The O-2 molecule is dissociated at the vacancy site of bridging oxygen and the oxygen atoms either fill a vacancy site or chemisorb at a fivefold-coordinated Ti4(+) site as an adatom. The latter is detected with much higher efficiency than the former. The O+ yield is increased during He+ bombardment of the reduced TiO2(110) surface due to formation of lower coordinated oxygen atoms. The oxygen species thus formed by ion bombardment or oxygenation are unstable pn the surface and tend to diffuse into bulk vacancy sites or higher coordination surface sites even at room temperature. (C) 2000 Elsevier Science B.V. All rights reserved.